Context adaptive directional intra prediction

Abstract

Enhanced directional prediction apparatus and methods are taught which are based on edge-based adaptive directional estimation, for providing an improved prediction direction for intra prediction within a coding device. Image gradient vectors are obtained for pixels in the neighborhood of the current block, and edge directions determined. Candidate edge directions are processed to derive a dominant edge direction in response to defining an objective function as a summation of projections to a candidate direction and computing suggested direction of each neighboring pixel. The dominant edge direction may be utilized for the prediction direction, such as in response to a detection mode flag signaled to the decoder, or modified by an angular adjustment, which can be communicated to a decoder.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority from U.S. provisional application Ser. No. 61 / 323,063 filed on Apr. 12, 2010, incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not ApplicableINCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC[0003]Not ApplicableNOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION[0004]A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, inclu...

AI Technical Summary

Benefits of technology

[0016]The present invention is directed at addressing the above intra prediction issues by extending direction prediction to improve the visual quality as well the coding performance for next generation video coding standards. Extended directional information is provided while leveraging inter-block geometric dependency at the decoder side to limit the need for additional side information. In particular, enhanced prediction direction detection is performed at the decoder-side in the reconstructed neighborhood of the current block to get the a priori prediction direction.

[0017]The encoder according to the invention can perform intra prediction encoding using any desired number of modes, such as beyond the nine modes provided in the AVC coding standard. The encoder can derive a prediction direction, which can be adjusted by the encoder to account for curvatures. Additional side information can be sent to the decoder to guide utilization of enhanced directional modes. In one implementation a signal is sent from the encoder to inform the decoder whether or not to reconstruct the image based on use of the extended modes, or to use the standard modes. In one implementation a flag referred to herein as “detection” is sent to the decoder to inform it that the directionality of the current block can be determined based on its neighbors. As the enhanced prediction direction detection is conducted at the decoder side, a high directional resolution can be obtained with the present techniques without requiring significant overhead in regard to the need for additional signaling bits.

[0028]An element of the invention is an intra predictive video coding method and apparatus which improves coding accuracy.

[0029]Another element of the invention is an enhanced edge-based adaptive direction estimation method which improves intra prediction.

[0031]Another element of the invention is enhanced directional prediction which can be applied at the decoder in response to neighboring blocks.

Problems solved by technology

First, the limited number of directional modes, such as a maximum of eight within AVC, can limit the precision necessary to properly code blocks subject to arbitrary directional patterns.

Secondly, mode number prediction from neighboring blocks is not sufficiently accurate to exploit the geometric dependency between blocks, which would allow use of enhanced directional modes in a decoder without significantly increasing side information.

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